Low-grade coal with a high moisture content has a low heating value. Therefore, a production method for obtaining refined-coal by dehydrating such low-grade coal by heating in oil has been developed (refer to JP-A No. H7-233383). This production method will be described referring to FIG. 2.
First, mixed oil including a heavy oil component and a solvent oil component is mixed with pulverized low-grade coil to obtain slurry S. The slurry S is preheated, and is thereafter supplied to a tank 21 (dehydration tank). The slurry S is drawn out from the bottom of the tank 21, is supplied to a heater 23 by a first pump 22, and is heated by high temperature vapor HV supplied from a compressor 24. By this heating, a part of the moisture and mixed oil present within pores of the low-grade coal evaporates. The heated slurry S and vapor V of water and oil are returned to the tank 21. Out of them, the vapor V is drawn out from the top portion of the tank 21, is compressed by the compressor 24, and becomes the high temperature vapor HV. This high temperature vapor HV is used as a heat carrier of the heater 23 described above, and becomes a condensed liquid L which is the mixture of the water component and the oil component. This condensed liquid L is fed to an oil separator 25, and is separated into the water component W and the oil component O. The water component W having been separated is discharged as the wastewater, and the oil component O having been separated is reused. Also, a part of the slurry S is fed to a post step (solid/liquid separating step and the like) from the first pump 22. By such production method, refined-coal which has been dried, contains heavy oil adhered within the pores, and has a high heating value can be obtained.
In this production method, the vapor V (mixed vapor of water and oil) generated by heating the slurry S is in a state of accompanying pores and mist-like splashes, and fine particles such as coal particles included therein are accompanied by the vapor V. Therefore, the fine particles are mixed in to the compressor 24 with the vapor V, and cause degradation of the performance and failure of the compressor 24. Accordingly, a technology has been proposed in which a defoaming tank 26 is arranged before the compressor 24 as shown in FIG. 3, oil (oil component O) of the liquid state is sprayed to the vapor V by a spray 27, and the pores are removed (refer to JP-A 2009-286900). Also, in the defoaming tank 26, a mist separator 28 for removing the splashes included in the vapor V after the pores have been removed is arranged. However, to spray oil to the vapor V is inefficient, and it is not easy to prevent mixing in of the fine particles to the compressor 24. Also, in the mist separator 28 arranged in the downstream of the spray 27, the fine particles included in the splashes can be captured to a certain extent. However, because the pressure loss and degradation of the capturing performance occur by adherence of the captured fine particles to the mist separator 28, frequent cleaning is required, and operability is insufficient.